1. Field of the Invention
This invention relates to a seat belt buckle particularly for vehicle safety seat belts for children.
The seat belt buckle according to the invention is of the type comprising a frame substantially enclosed by a casing and having a latch member pivotally mounted to the frame, which is biased to a position of engagement by means of a pressure spring mounted between the frame and the latch member, for engagement with a tongue member inserted into the buckle, said latch member being operable against the bias of the pressure spring to a disengaged position for releasing the tongue member.
2. Description of the Prior Art
In prior art seat belt buckles of this type there is displaceably mounted in the casing a push button for operating the latch member. This push button is accessible through an opening of the casing to be depressed by the finger against the bias provided by said pressure spring when it is desired to release the tongue member from the buckle. A seat belt buckle of this type is disclosed in U.S. Pat. No. 3,774,268 to Holmberg.
The pressure spring of the buckle determines the pressure that has to be exerted on the push button for releasing the tongue member from the buckle. Accordingly, the force of this spring is chosen with consideration of the requirement that the tongue member must not be disengaged due to an unintended light pressure against the push button for example in a collision or under heavy braking and that the buckle shall at the same time be easily and readily operated not only when the safety belt is being taken off but also when it is being put on; the bias provided by the pressure spring, possibly combined with the bias provided by ejection springs, if any, determines the pressure that has to be exerted between the buckle and the tongue member as they are being pushed together when the safety belt is being put on.
In practice it has been found that it is possible to have a rather low operating pressure without neglecting the safety against unintended disengagement of the tongue member except in one case, viz. in case of push button buckles of vehicle or automotive seat belts for children such as are used in special seats for children. Small children often have a tendency to touch things and, therefore, cannot refrain from touching also the seat belt buckle, which in that case can result in depression of the push button so that the tongue member will be released. Should this happen once it is most likely that the child will find some pleasure in depressing the push button repeatedly to release the tongue member which means that the driver or the passengers must keep on securing the child again, and moreover involves a considerable risk that the child is not at any time secured by means of the seat belt and therefore, in an emergency, may lack the necessary protection.
Tests have shown that a child less than five years old is not able to disengage a push button buckle requiring a disengagement pressure of about 7 kg or more. In most cases a disengagement pressure of about 7 kg or more excludes every risk that the child will manage to disengage the buckle on its own but does not necessarily provide any difficulties for an adult (provided, of course, that the pressure required is held within reasonable limits).